1. Field of the Invention:
The present invention relates to a method of and apparatus for detecting an end point of plasma treatment, and more particularly to a method of and apparatus for detecting an end point of plasma treatment which is suitable for detecting the end point of the reaction of plasma treatment of a specimen such as the substrate of a semiconductor device by selecting plasma spectrum having a characteristic wavelength from the plasma spectrum occurring at the time of reaction of plasma treatment of such a specimen and by making a judgment from the change of the quantity of the plasma light selected vis-a-vis the reaction time of the plasma treatment.
2. Description of the Prior Art:
As a method of detecting the end point of the reaction of plasma treatment of a specimen such as a semiconductor device substrate by selecting plasma spectrum having a characteristic wavelength from the plasma spectrum occurring at the time of the reaction and by detecting the same from the change of the quantity of the plasma spectrum selected vis-a-vis the reaction time of the plasma treatment, there is known, for example, one which is disclosed in Japanese Patent Laid-Open No. 115536/1981. This method is described hereinafter with reference to FIG. 1.
In FIG. 1, a curve `a` indicates the intensity of radiation corresponding to a reaction product. In other words, the radiation corresponding to the reaction product increases sharply on starting the reaction, reaches its normal state within a brief period of time, decreases sharply on the end of the reaction, and then assumes its normal state. In this case, the end point of the plasma treatment reaction is detected at the point of time when the quantity of radiation corresponding to the reaction product, i.e., the quantity of plasma spectrum, has decreased sharply following the reaction's end and has assumed its normal state, namely, at the point of time when the differential value `b` of a function of the quantity of plasma spectrum/reaction time has reached a predetermined level 1.
According to such a method, it is possible to detect the end point of the reaction of plasma treatment with good accuracy in a case where a curve of change in the reaction time of the quantity of plasma spectrum is similar to the one described above. However, in a case where the curve of change in the reaction time of the quantity of plasma spectrum fails to become similar to the one described above, and in a case where the magnitude of the level is large, there is a possibility that the differential value of a function of the quantity of spectrum/reaction time during the course of plasma treatment may reach the predetermined level, with the result that the end point of plasma treatment is detected by mistake in the course of plasma treatment. If the curve of change in the reaction time of plasma spectrum fails to become like the one described above, and if the magnitude of the level is, to the contrary, small, there is a possibility that the differential value of a function of the quantity of plasma spectrum/reaction time may fail to reach the predetermined level, with the result that it becomes impossible to detect the end point of the reaction of the plasma treatment. Thus, in a case where the curve of change in the reaction time of the quantity of plasma spectrum fails to show a curve as the one described above, there has been a drawback in attempts to detect with satisfactory accuracy the end point of the reaction of plasma treatment.